In this Program Project Grant our overarching hypothesis is that alterations in the assembly states and mechanical properties of cytoskeletal IF, specifically the type III IF composed of vimentin (VIF), play important roles in regulating the micromechanical properties of cells in response to mechano- and chemo- signaling. These studies are critically important as IF are major elements of the cytoskeletal system of mammalian cells and yet their specific functions in cell motility remain unknown. The 6 Project Leaders, and their research aims are as follows: R. Goldman, Northwestern University, will determine how the vimentin IF (VIF) system changes in response to mechanical and chemical signals, and will purify and characterize the vimentin precursors that form as VIF assemble and disassemble. V. Gelfand, Northwestern University will determine the relationship between VIF with microtubules and actin filaments, identify the molecular motors responsible for translocating VIF precursors, and investigate how VIF affect cytoskeletal dynamics and microtubule (MT) dynamics. G. Danuser, Harvard University, will test the hypotheses that VIF network formation involves a spatially distributed assembly line, that this process involves molecular motors, and that VIF network assembly modulates assembly of MT and microfilaments (MF). D. Weitz, Harvard University, will determine the micromechanical properties of in vitro assembled VIF networks prepared from purified vimentin, native VIF networks isolated from cells and in living cells. P. Janmey, University of Pennsylvania, will determine how the VIF network contributes to the micromechanical properties of living cells and how this changes in response to substrate stiffness and external forces. P. Burkhard, University of Connecticut, will use biophysical techniques and X-ray crystallography to determine the structure and biophysical properties of the vimentin dimer and study the formation of VIF assembly intermediates. In all of these studies, the regulatory function of different posttranslational phosphorylation events will be examined.